Contact lens having a uniform horizontal thickness profile

ABSTRACT

A contact lens having a rotational stabilization mechanism thereon, such as prism ballast, and a thickness profile that reduces the torque imparted on the lens by the action of the eyelids, especially for stabilizing toric lenses. The prism ballast is provided on one or more portions of the anterior face of the lens such that the lens body has a uniform thickness of within 10% along horizontal cross-sections. The anterior face of the lens may be segregated into a peripheral zone, an inner zone circumscribed by the peripheral zone, and a central optic zone. The prism ballast portion is provided within the inner zone, which may be further subdivided into a superior portion, an intermediate portion proximate the optic zone, and an inferior portion. The ballast portion increases in thickness along a superior-inferior line parallel to a vertical meridian, and has a substantially uniform thickness perpendicular thereto. The peripheral zone may be tapered, and have a rounded edge. The rate of thickness change across any portion of the peripheral zone is less than about 250 μm/mm.

RELATED APPLICATION

This is a continuation of application Ser. No. 09/818,244 filed Mar. 27,2001, now U.S. Pat. No. 6,467,903 which claims the benefit of U.S.provisional application No. 60/193,493, filed Mar. 31, 2000. Thedisclosure of each of these applications is incorporated in its entiretyherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to contact lenses and, in particular, toan improved ballast, preferably a prism ballast, for toric lenses thatimposes a low-torque rotational correction on the lens.

Astigmatism is a defect in the eye that is corrected by a lens with anon-spherical prescription. The prescription, which is usually expressedas cylinder on the patient's prescription order, causes at least aportion of the surface of the lens to have the shape of the toricsegment. A torus is a surface or object defined by the rotation of acircle about an axis other than its own. For example, a donut has atoroidal shape. The toric portion of the lens is a small oval-shapedsection of the toroid, with a major axis and a minor axis. As a resultof this non-axi-symmetric configuration, proper rotational orientationof the lens must be maintained. It should be noted that other lenses,for instance that provide bifocal or multi-focal correction, arenon-axi-symmetric and thus have a particular orientation outside ofwhich performance suffers.

Astigmatism is often associated with other refractive errors such asmyopia or hypermetropia, and so toric contact lenses often also providesome spherical correction, negative or positive. While the concave orposterior surface of a contact lens generally has a sphericalconfiguration, where the lens is used to correct astigmatism theposterior surface will usually have the toric configuration. That is,the curved portion of the posterior surface of the lens has a major axisand a minor axis. The radius of curvature of the posterior surface ofthe lens is larger in the major-axis direction than in the minor-axisdirection. The major diameter of the toric surface is generally smallerin diameter than the overall lens, and is cut into a starting sphericalbase curve. Additionally, the anterior and/or posterior surface(s) ofthe optical zone may include a spherical portion that contributes to adistance refractive correction. The spherical correction is typicallyprovided on the exterior or anterior surface. Of course, certainprescriptions provide the toric curve on the anterior surface, with thespherical correction also on the anterior surface, or on the posteriorsurface.

While spectacle lenses are held rigidly in place by a frame, toriccontact lenses must be stabilized so that the cylindrical correction isstabilized in substantially the correct position on the eye. Softcontact lenses which had been designed for use to correct astigmatismare well-known in the art. Generally, these lenses rely on some type ofballasting or stabilizing method to cause the lens to be properlyoriented in the eye. The ballast is typically provided on a contact lensby incorporating structures either on the front surface or on the backsurface, or spread between both surfaces. Such orientation structuresutilize eyelid forces generated during blinking. As the eyelids wipeacross the contact lens, they tend to squeeze the lens down and againstthe cornea and displace elevated surface features.

A so-called “wedge” or “prism” ballast may be utilized wherein the loweror inferior portion of the lens is relatively thicker than the upper orsuperior portion. As a result, the upper eyelid, which undergoes greatermovement than the lower eyelid, and thus exerts greater influence on thecontact lens, tends to displace the inferior portion of the contact lensdownward, inherently rotating the contact lens over the cornea into theintended orientation. Alternatively, the lens may incorporate aso-called “periballast” (short for peripheral ballast) stabilizationthat involves a ballast region surrounding but excluding the centraloptic.

For examples of prism ballast, see U.S. Pat. Nos. 4,573,774, 5,125,728,and 5,020,898, and PCT Publication No. WO 98/45749. Another orientationstructure for contact lenses includes the provision of thin superior andinferior zones relative to a thicker central zone. Such structures areshown in U.S. Pat. Nos. 4,095,878, and 5,650,837. Alternatively,channels or ridges may be provided on the contact lens, such as seen inPCT publication No. AU 92/00290.

U.S. Pat. No. 5,020,898 describes a toric contact lens with ballastdistributed outside the anterior optical zone such that the ballastthickens from the top of the lens to two points of maximum thicknessproximate the lower peripheral edge.

U.S. Pat. No. 5,125,728 also describes a ballast portion that increasesfrom a superior part of the lens to a maximum thickness in the lowerperiphery on each side thereof. The maximum thickness of the ballast islocated as close as possible to the lens edge so that these portions fitover the peripheral cornea and conjunctiva to limit lens rotation. Aballast-free corridor of least resistance is provided in the verticalmid-section of the lens above and below the central optical area. Thepatent asserts that the ballast-free corridor in combination with thethicker ballast and thicker portions close to the lens peripheryprovides an improved stabilization mechanism.

Finally, PCT Publication No. WO 98/45749 describes a ballast lens with aprism through the optical zone. The anterior and posterior optical zonediameters are selected such that when combined to form a lens, thethickness at the superior and inferior junctions of the optical zone onthe anterior face is controlled.

In addition to the relative ability of a lens to orient consistently oncornea, other factors affect the performance of the variousstabilization structures. For example, some structures are better thanothers with respect to one or more of the following: reducing theoverall thickness across the toric contact lens for the physiologicalbenefit of the wearer, ease of manufacture, reducing the lens parameterinventory, clinical performance including wearer comfort and consistencyof fitting between refractive powers. With respect to wearer comfort, ingeneral, the thinner the lens and the smoother the surface, the morecomfort will be provided. In addition, it is known to provide aperiphery on the lens that is relatively thin and shaped for addedcomfort.

The principal limitation of existing toric contact lens designs is thatorientation is highly variable and/or uncomfortable, for a given design,between individual toric lens wearers. Besides the lens design and lensmaterial, patient factors also influence the orientation of a toriccontact lens on the eye and contribute to this variability in lensorientation. Patient factors such as blink characteristics and ocularparameters such as eyelid, corneal, and conjuctival shape and anatomymay result in undesired interaction (for example, asymmetry) orinsufficient interaction with the contact lens. However, many of theproblems associated with prior art mechanisms may be attributed toproblems with failure of the stabilization mechanism to maximize eyelidinteraction and reduce the variability of lens orientation betweenindividuals.

Despite much effort in this area, there is still a need for a toriccontact lens that has more consistent stabilization features betweenindividuals.

SUMMARY OF THE INVENTION

In accordance with the present invention, a contact lens having improvedthickness and ballast arrangement is provided. The contact lens of thepresent invention reduces the known variability of lens orientation fromindividual to individual. Further, the lenses of the present inventionprovide more effective interaction between the stabilization mechanismand the eyelid during blinking, and preferably include a peripheral zonethat is required for wearer comfort.

In one aspect, therefore, the present invention provides a contact lens,including a contact lens body having a generally spherical basecurvature with a convex anterior face, a concave posterior face, and aperipheral edge therebetween. A peripheral zone is defined adjacent theperipheral edge of the anterior face. The body has a thickness betweenthe anterior face and the posterior face and is non-axi-symmetric so asto define a superior edge and an inferior edge. Further, a verticalmeridian is defined from the superior edge toward the inferior edge anda horizontal meridian is defined perpendicular thereto. The anteriorface defines a plurality of zones thereon, including an inner zonecircumscribed by the peripheral zone, and an optic zone definedgenerally in the middle of the inner zone. Additionally, the lensincludes a prism ballast portion whereby the thickness increasesparallel to the vertical meridian from the superior edge toward theinferior edge in at least a ballast portion of the inner zone. The innerzone comprises a superior portion between the optic zone and thesuperior extent of the inner zone, an inferior portion between the opticzone and the inferior extent of the inner zone, and an intermediateportion between the superior and inferior portions. The ballast portionis defined within one or more of the superior, intermediate, andinferior portions and has a series of consecutive horizontalcross-sections exclusive of the peripheral zone and optic zone spanninga distance along the vertical meridian of at least 20% of the smallestdimension of the superior, intermediate, and inferior portions asmeasured along the vertical meridian, wherein each horizontalcross-section has a substantially uniform thickness not varying by morethan about 30 μm or 20%, whichever is greater in absolute terms. In oneembodiment, the thickness of the contact lens in each of the consecutivehorizontal cross-sections does not vary by more than about 15 μm orabout 10%, whichever is greater in absolute terms.

In one embodiment, the ballast portion is defined wholly within only oneof the superior, intermediate, and inferior portions. In anotherembodiment, the ballast portion is defined wholly within only two of thesuperior, intermediate, and inferior portions. In still anotherembodiment, the ballast portion is defined within all three of thesuperior, intermediate, and inferior portions, or comprises the entireinner zone.

In a preferred embodiment, a rate of change of thickness in the taperedperipheral zone is less than about 250 μm/mm, more preferably less thanabout 200 μm/mm.

In an alternative embodiment, a contact lens of the present inventioncomprises a contact lens body having a generally spherical basecurvature with a convex anterior face, a concave posterior face, and aperipheral edge therebetween. A peripheral zone is defined adjacent theperipheral edge of the lens that tapers thinner toward the peripheraledge of the lens. The lens body has a thickness between the anteriorface and the posterior face and is non-axi-symmetric so as to define asuperior edge and an inferior edge. A vertical meridian is defined fromthe superior edge toward the inferior edge and a horizontal meridian isdefined perpendicular thereto. The anterior face defines a plurality ofzones thereon, including an inner zone circumscribed by the peripheralzone and having a prism ballast portion therein, and an optic zonedefined generally in the middle of the inner zone, wherein the isthickness increases parallel to the vertical meridian from the superioredge toward the inferior edge in at least the prism ballast portion ofthe inner zone. Along a 225° meridian, the distance between the innerzone and the peripheral edge is less than about 1.4 mm.

In accordance with one aspect of the invention, a molded contact lensincludes a fully molded contact lens body (i.e., molded on both theanterior and posterior faces) having the general features as describedabove. As before, the molded lens has a prism ballast portion in theinner zone and, along a 225° meridian, the distance between the innerzone and the peripheral edge is less than about 1.8 mm. Alternatively,or desirably in addition, and along a 270° meridian, the distancebetween the inner zone and the peripheral edge is less than about 2.1mm, while along a 180° meridian, the distance between the inner zone andthe peripheral edge is less than about 1.3 mm.

Desirably, a band circumscribed by the peripheral zone and around theoptic zone is substantially annular. Namely, a superior distance A isdefined along the vertical meridian and within the inner zone from theoptic zone to the peripheral zone. An inferior distance B is definedalong the vertical meridian and within the inner zone from the opticzone to the peripheral zone. For molded prism ballasted lenses the bandis annular within the range of 0.33A≦B≦A, while for all prism ballastedlenses the annular band is within the range of 0.55A≦B≦A.

Each and every feature described herein, and each and every combinationof two or more of such features, is included within the scope of thepresent invention provided that the features included in such acombination are not mutually inconsistent.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin connection with the accompanying illustrative drawings in which likeparts bear like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front elevational view of a contact lens accordingto the present invention illustrating various zones defined thereon;

FIG. 2 (A-A′ to E-E′) illustrate a series of horizontal cross-sectionstaken through the lens of FIG. 1;

FIG. 3 is a graph showing the varying thickness of the contact lens ofFIG. 1 taken along a vertical meridian Z-Z′;

FIG. 4 a is a schematic diagram of the contact lens of the presentinvention having an exemplary topographical numerical thickness mapsuperimposed thereon;

FIG. 4 b is a graph of a portion of the contact lens of the presentinvention illustrating a discontinuity and angular relationship betweenzones thereon;

FIGS. 5 a-5 d are elevational views of contact lenses of the presentinvention each having a spherical anterior optical zone and varyingregions of substantially uniform horizontal thickness;

FIGS. 6 a-6 d are elevational views of contact lenses of the presentinvention each having a toric anterior optical zone and varying regionsof substantially uniform horizontal thickness;

FIG. 7 is a schematic front elevational view of a contact lens having anumber of meridian lines superimposed thereon for reference; and

FIG. 8 is a schematic front elevational view of a contact lens of theprior art illustrating various zones defined thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides stabilized contact lenses, especiallycontact lenses having a cylindrical correction for astigmatism. Morebroadly, the present invention provides contact lenses having elevatedsurfaces thereon that interact with the blinking action of the eyelidsto rotationally stabilize the lens. The rotational stability is usefulfor any contact lens that is non-axi-symmetric. For example, therotational orientation of toric lenses or multifocal lenses must bemaintained for proper correction. It should be understood, however, thatrotational stability may also be desirable for other specialized lenses.

In the following description, a number of surfaces and thicknesses ofthe contact lenses of the present invention will be described withreference to schematic elevational views of the lenses, in that thelenses have been flattened. Contact lenses typically possess anunderlying spherical curvature, with the anterior face being convex, andthe posterior face being concave. The various surfaces and optic zonesare then either molded or machined from the base sphere. For simplicity,the elevational views shown herein are flattened, with the base sphereremoved. In this way, the lines of shading corresponding to theunderlying spherical curvature are removed so that the particularsurfaces and thicknesses of the present invention can be more clearlyillustrated. In a preferred embodiment, lenses of the present inventionhave a negative spherical power distance correction, and a toric surfacefor cylindrical correction.

An exemplary contact lens 20 of the present invention is thus shown inschematic elevational view in FIG. 1 flattened without shading toillustrate various zones thereon. The lens 20 includes a lens body ofsuitable soft or rigid material. Soft contact lenses are typically madeof a hydrophilic material such as hydroxyethylmethacrylate,metallo-organic substances, silicone rubbers, silicone hydrogels,urethanes, etc. Alternatively, a rigid gas-permeable material such assiloxane acrylate or fluorosiloxane acrylate may be used. The lens bodyhas an overall spherical curvature with a concave posterior face adaptedto contact the cornea opposite an outwardly-facing convex anterior face.

With reference to FIG. 1, the lens 20 includes an optic zone 22, aperipheral zone 24, and an inner zone 26 circumscribed by the peripheralzone, wherein the optic zone 22 forms a portion of the inner zone 26.Alternatively, the inner zone 26 may be defined between the optic zoneand the peripheral zone. As will be described further herein, the opticzone 22 may be circular, toroidal, or other special shapes. Theperipheral zone 24 may have a uniform radial dimension (width), or theradial dimension may vary. In the exemplary illustrated embodiment, theperipheral zone 24 has a narrower radial dimension at a superior end 30,and a wider radial dimension at an inferior end 32. Stated another way,the inner zone 26 has a circular periphery or ballast periphery 34 thatis slightly offset toward the top of the lens 20 along a verticalmeridian or centerline Z-Z′ therethrough. It should be noted that theclear delineations in the drawings between the optic zone 22 peripheralzone 24 and inner zone 26 should not be taken to imply that there is adiscontinuity or corner at those locations, and in fact the exemplarylens of the present invention possesses gradually curved transitionsbetween the zones.

A lens edge 36 defines the intersection of the anterior and posteriorfaces. The peripheral zone 24 desirably exhibits a taper so as to bethinner at the lens edge 36 than at the circular ballast periphery 34.In this regard, the peripheral zone 24 preferably defines a partialconical surface (albeit, superimposed on the underlying sphericalcurvature). Alternatively, the peripheral zone 24 may define a partialspherical or other curvature (i.e., shape), for example, any suitablecurvature.

Various features of the lens 20 are believed to enhance wearer comfortin comparison to other similar lenses. Indeed, certain clinical trialsresulted in findings that patients responded more favorably to questionsdesigned to ascertain a comfort level of lenses made according to thepresent invention than with respect to questions on the comfort level ofsimilar lenses.

The inner zone 26 may be segregated into three parts along the verticalmeridian Z-Z′. Specifically, a superior portion 40 extends between theupper extent of the ballast periphery 34 and the upper extent of theoptic zone 22, delineated by an imaginary line 42, perpendicular to thevertical meridian Z-Z′. An intermediate portion 44 extends between theperpendicular line 42 and a second perpendicular line 46 at the lowerextent of the optic zone 22. Finally, an inferior portion 48 extendsbetween the perpendicular line 46 and the lower extent of the ballastperiphery 34. The optic zone 22 thus lies entirely within theintermediate portion 44.

The superior portion 40, intermediate portion 44, and inferior portion48 are used in the present application to segregate the inner zone 26into discrete areas in which specific ballast surfaces can be provided.It should be understood, however, that the dividing lines 42, 46 betweenthe areas may be shifted, or may be non-linear, for that matter. In oneaspect, the present invention concerns particular ballast or prismballast surfaces/thicknesses in one or more portions of the inner zone26, which portions may be defined in a number of ways. Therefore, thereader will understand that the portions 40, 44, and 48 are shown asexemplary only. Desirably, iso-thickness ballast surfaces are formed inat least 20% (measured as a percent of the vertical dimension),preferably at least 50%, and more preferably at least 100%, of at leastone of the portions 40, 44, and 48. More specifically, an iso-thicknessprism ballast portion is defined within one or more of the superior,intermediate, and inferior portions 40, 44, and 48 as a series ofconsecutive horizontal cross-sections-exclusive of the peripheral zoneand optic zone spanning a distance along the vertical meridian of atleast 20% of the smallest dimension of the superior, intermediate, andinferior portions as measured along the vertical meridian. The term“iso-thickness” means that each of the consecutive horizontalcross-sections has a substantially uniform thickness not varying by morethan about 30 μm or 20%, whichever is greater in absolute terms. In aparticularly preferred construction, ballast surfaces are provided in atleast two, more preferably all three of the portions 40, 44, and 48.

The present invention pertains to contact lenses having rotationalstabilization mechanisms thereon, including those with ballasts, e.g.,prism ballasts, periballasts, and so-called “dynamically stabilized”lenses. A ballasted lens provides some raised surface contour over whichthe eyelid wipes to re-orient the lens, generally about its opticalaxis. A prism ballast provides a wedge or tapered ballast forinteraction with the eyelids even in the optic, while a periballast isexclusive of the optic. Dynamic stabilization involves superior andinferior flats on the lens leaving a thickened midsection to interactwith the eye, as seen in U.S. Pat. No. 4,095,878. Those of skill in theart will also recognize that there may be other such stabilizationmechanisms with which the present invention could be advantageouslyused.

FIG. 1 also illustrates a number of representative cross-sectional linesA-A′, B-B′, C-C′, D-D′, and E-E′ extending perpendicularly with respectto the vertical meridian Z-Z′ (i.e., horizontally). These sections areillustrated in FIG. 2, with the base spherical curvature shown. Thepresent invention provides that consecutive horizontal cross-sectionsshown in FIG. 2 that possess ballast each has a substantially uniform oriso-thickness, except in the optic zone 22 and peripheral zone 24. Forexample, one of the cross-sections in FIG. 2 having ballast, such asD-D′, has a substantially uniform thickness. Alternatively, all of thecross sections shown in FIG. 2 that possess ballast may have a uniformthickness except in the optic zone 22 and peripheral zone 24.

Desirably, the sections of substantially uniform thickness do not varyin thickness within one section by more than about 30 μm or about 20%whichever is greater in absolute terms. In one embodiment, the thicknessof the sections varies by no more than about 15 μm or about 10%, such asby no more than about 10 μm or about 7%, whichever is greater. Suchvariations will be understood to be sufficiently small that the sectionscan still be regarded as being of “substantially uniform” thickness.

In an exemplary embodiment of the present invention, the contact lens 20has a so-called prism ballast superimposed thereon within the entireinner zone 26. That is, from the intersection of the ballast periphery34 with the vertical meridian Z-Z′ at the top of the lens 20, to theintersection between the same two lines at the bottom of the lens, thethickness generally increases. This thickness distribution along thevertical meridian Z-Z′ is graphically illustrated in FIG. 3, with thesuperior end 30 of the peripheral zone 24 shown at the right and theinferior end 32 shown at the left. Starting at the right side, the taperof the peripheral zone 24 within the superior end 30 from the edge 36 tothe upper extent of the ballast periphery 34 is seen. In the superiorportion 40, the thickness gradually increases to the horizontal line 42.The thickness further increases through the optic zone 22 to thehorizontal line 46. The greatest thickness is in the inferior portion 48to the lower extent of the ballast periphery 34. The lens again tapersdownward within the peripheral zone 24 between the ballast periphery 34to the inferior edge 36.

The thickness distribution represented in FIG. 3 thus corresponds to aprism ballast within the lens 20 that extends through all of thesuperior portion 40, intermediate portion 44, and inferior portion 48.Indeed, even the optic zone 22 exhibits this prism ballast. Importantly,the present invention provides a prism ballast in at least one of theseportions 40, 44, 48 having horizontal cross-sections of uniformthickness. Therefore, as seen in FIG. 2, all of the cross-sectionsillustrated have uniform thicknesses along their widths, except in theperipheral zone 24. Of course, because of the increasing thickness inthe superior-inferior direction parallel to the vertical meridian Z-Z′,the thickness of each cross-section increases from cross-section A-A′ tocross-section E-E′.

The uniform thickness in the horizontal cross-sections helps tostabilize lenses of the present invention, in contrast to previouslenses. More specifically, lenses of the present invention are suitablefor a greater number of wearers than those of the prior art because ofthe lower torque exerted by the eyelids on the lens by virtue of theuniform thickness or iso-thickness configuration. The iso-thicknessballast arrangement maximizes eyelid interaction by achieving an evencontact across each section of the lens as the eyelid travels down andup the lens during blinking. In contrast, the eyelid generates morerotational torque during a normal blink when interacting with horizontallens sections of non-uniform thickness, as in the prior art. This isbecause for a lens to orient appropriately on the eye the lens-eyelidinteraction should be maximized across the lens (i.e., across eachhorizontal cross-section) so that the lens is squeezed into the desiredorientation (overall orientation) and undergoes minimal fluctuationduring blinking (interblink orientation).

Prior art lenses, having narrow peaks or points of maximum thickness oneither side of the vertical meridian are more likely to create anon-uniform lens-eyelid interaction across horizontal sections. Inaddition, the horizontal distance between peaks of maximum thickness inthe prior art lenses typically increases from a superior portion to thehorizontal midline, and then decreases from the mid-line to the inferiorportion. This further varies the lens-eyelid interaction forces.

The uniform thicknesses in the horizontal cross-sections of the lens 20have proven to enhance performance of the lenses in comparison to othersimilar lenses in terms of maintaining a correct rotational orientationin the eye. Clinical trials have shown that there is less variability inthe position of a location mark on the lens over time. For example,groups of 20 people at a time were studied to determine the positions oflocation marks over time on various lenses in the eye, and the standarddeviations of the positions of the location marks were determined. Theresults are that the standard deviation for lenses of the presentinvention are measurably smaller than in other lenses, meaning thepresent lenses had less rotational instability in the eye.

Exemplary values for the thickness of the contact lens 20 having thedistribution as seen in FIG. 3 are provided in the topographicaldepiction of FIG. 4 a. It is understood that the contact lens 20 shownin FIG. 4 a is generally circular. In FIG. 4 a, the inner zone 26 isdivided by horizontal and vertical grid lines into a plurality ofdiscrete units. Each horizontal row of units has a uniform thicknessthroughout the inner zone 26. On the other hand, the thickness along avertical column of units generally increases from the superior to theinferior. For example, horizontal row 50 has a uniform thickness of 140μm other than in the optic zone. Vertical column 52 has a thickness of70 μm at the top, gradually increases to 280 μm, and begins to decreasejust prior to the inferior portion of the peripheral zone 24. The valuesprovided in FIG. 4 a are exemplary and are suitable for a soft hydrogelcontact lens. The values for lenses made of other materials may varydepending on the optical or other properties of the particular material.

It will be understood by the reader that the discrete units mapped inFIG. 4 a represent the average thickness within each unit. That is, thethickness down the lens 20 changes gradually, rather than at a steppedborder between units. More generally, although the present applicationdescribes distinct zones or portions in contact lenses, those zones areshown for clarity of description of the invention only. It will beappreciated by those skilled in the art that there are no sharpdistinctions between these different zones of the lens, but that theyare instead smoothly blended into one another.

FIG. 4 a also illustrates the decreasing thickness or taper of the lens20 through the peripheral zone 24. For example, at the inferiormidpoint, the thickness decreases from 210-140-70 μm. This is also seenin the graph of FIG. 3. This taper within the peripheral zone 24provides a so-called comfort zone around the edge of the lens 20.Because of the reduced thickness, movement of the eyelids across thecontact lens is facilitated, and there is less irritation. Specifically,the eyelids more easily travel over the tapered peripheral zone 24 thanif there were a more abrupt thickness change.

In an exemplary embodiment, the lens 20 has a corneal fittingrelationship to maintain the lens centered on the cornea. The preferredlens has a diameter sufficient to achieve corneal coverage, and optimumstability is provided so that the lens does not become loose andunstable with gaze and blinking, which may influence the comfort andvision of the wearer. The sagittal depth (concave depth of the posteriorface) for an optimum lens-cornea fitting relationship is between about3.0 and 5.0 mm over a lens diameter of between about 13.0 mm and 16.0mm. The lens diameter is more preferably between about 13.5-14.8 mm. Apreferred thickness of the lens edge 36 is less than about 120 μm, morepreferably about 90 μm. In this respect, the thickness is measuredradially with respect to the curvature of the anterior face. The extremeoutermost extent of the edge 36 may incorporate a preferred rounding ofthe anterior edge corner.

A plurality of meridian lines may be defined through the center of thelens. In a preferred embodiment, for maximum wearer comfort, the rate ofchange in lens radial thickness from the end of the ballast zone 34 tothe lens edge 36 (i.e., in the peripheral zone 24) is less than about250 μm/mm along any meridian of the lens. For example, in thetopographical map of FIG. 4 a, the rate of change of thickness along anymeridian and within the peripheral zone 24 is less than about 250 μm/mm.More preferably, the rate of change in the peripheral zone 24 is lessthan about 200 μm/mm.

The advantageous interaction between the peripheral zone 24 and theiso-thickness is further exemplified in the proximity to the lens edge36 of the point of maximum thickness, as variously measured around thelens. To illustrate this principle, FIG. 7 shows various meridiansthrough the optical axis and around the lens in degrees, starting at the3:00 o'clock position and moving counterclockwise. Of course, withiso-thickness in the inner zone 26, the point of maximum thickness alongany horizontal meridian corresponds to the thickness along the entirehorizontal meridian excluding the optical zone. Therefore, the beginningof the inner zone 26 and the point of maximum thickness along anymeridian always lies on the ballast periphery 34. However, because ofthe preferred ballasting, the maximum thickness changes around theballast periphery 34.

For prism ballasted lenses in accordance with the present invention, andalong the 225° meridian, the distance between the point of maximumthickness (e.g., the ballast periphery 34) and the lens edge 36 is nogreater than about 1.4 mm, regardless of the thickness. For any type ofballasted lens, the maximum thickness along the 225° meridian inaccordance with the present invention is between about 200-4000 μm,preferably between about 250-350 μm, and more preferably about 320 μm.Along the 270° meridian, the distance between the point of maximumthickness (e.g., the ballast periphery 34) and the lens edge 36 is nogreater than 1.8 mm, also regardless of the thickness, though athickness of about 320 μm is preferred. For fully molded prism ballastedlenses (i.e., molded on both the anterior and posterior faces), andalong a 225° meridian, the distance between the point of maximumthickness (e.g., the ballast periphery 34) and the peripheral edge isless than about 1.8 mm, and desirably, along a 270° meridian, thedistance between the point of maximum thickness and the peripheral edgeis less than about 2.1 mm. Also, along a 180° meridian, the distancebetween the inner zone and the peripheral edge is less than about 1.3mm. In general, the peripheral zone 24 of the lenses of the presentinvention is relatively narrow in comparison to the prior art ballastedlenses, yet because of the preferred thicknesses the comfort taper anglein the peripheral zone 24 is relatively shallow, as mentioned above.

Although the preferred lens of the present invention has smooth, roundedtransitions between different portions thereon, discrete boundaries orcorners are not excluded. For example, the transition between theperipheral zone 24 and the inner zone 26 may be defined by a roundedcorner or discontinuity at the circular ballast periphery 34. An exampleof the transition between the ballast area 26 and the peripheral zone 24(i.e., at 34) along the meridian Z-Z′ is seen in FIG. 3.

FIGS. 5 a-5 d illustrate several variations of the contact lens of thepresent invention having different ballast portions defined within theballast zone. For purpose of explanation, the reader will refer back toFIG. 1 for the definition of the various portions (i.e., superior,intermediate, and inferior) of the inner zone 26. FIG. 5 a shows acontact lens 70 having a ballast portion 72 defined within the superiorportion of the inner zone. Again, the inner zone lies between an opticzone 74 and a peripheral zone 76. FIG. 5 b illustrates a contact lens 80of the present invention having a ballast portion 82 defined within boththe superior and intermediate portions of the inner zone. FIG. 5 c showsa contact lens 90 having a ballast portion 92 defined within the entireinner zone, through the superior, intermediate, and inferior portionsthereof. Finally, FIG. 5 d illustrate a contact lens 100 having aballast portion 102 defined only within the inferior portion of theinner zone.

Other variations not shown include a ballast portion defined whollywithin either the intermediate or inferior portions of the inner zone,or within the intermediate and inferior portions combined, exclusive ofthe superior portion. Also, the ballast portion could surround the opticzone in a so-called “periballast” arrangement, or could continue throughthe optic zone in a so-called “prism ballast” arrangement.

FIGS. 6 a-6 d illustrate a number of other contact lenses of the presentinvention having a cylindrical correction on the anterior face thereof.More specifically, a toric optic zone 110 is shown in each of the lensesoriented along a major axis 112 that is rotated with respect to thesuperior-inferior axis of the lens. The need for proper ballasting forthe lenses is thus apparent to maintain the proper offset orientation ofthe axis 112.

FIG. 6 a shows a contact lens 120 having a ballast portion 122 beginningin the superior portion and continuing through both the intermediate andinferior portions of the inner zone. FIG. 6 b shows a contact lens 130having a ballast portion 132 located entirely within the inferiorportion of the inner zone. FIG. 6 c depicts a contact lens 140 having aballast portion 142 wholly within the intermediate portion of the innerzone. Finally, FIG. 6 d shows a lens 150 having a ballast portion 152only within the superior portion of the inner zone.

FIG. 8 shows a prism ballast lens of the prior art (CooperVisionFrequency Xcel (Encore) Toric) with lines demarking the transitionsbetween various zones drawn. Specifically, an optic zone 200 isseparated from a ballast zone 202 by a generally circular inner line204, and the ballast zone is separated from a peripheral zone 206 by agenerally circular outer line 208. While the inner line 204 isapproximately centered as expected on the optical axis OA, the outerline 208 is offset upward along the vertical meridian 210. As a result,the ballast zone 202 is wider in the superior region than the inferior.Specifically, the superior radial width A of the ballast zone 202 issignificantly greater than the inferior radial width B. Indeed, thesuperior radial width A is more than twice the inferior radial width B.

In contrast, as seen in FIG. 1, the lenses of the present invention havean inner zone 26 that is substantially annular, with a radial dimensionA that is within about 300% of the radial width B. That is, for moldedprism ballasted lenses the band is annular and the relationship0.33A≦B≦A holds. Alternatively, for all prism ballasted lenses theannular band is within the range of 0.55A≦B≦A.

It will be appreciated that the present invention may be embodied inlenses having varying optical powers. For example, a contact lens ofpresent invention may have an optic power of about between about −8 toabout +8 diopters, although this range is not to be considered limiting.

Additionally, the contact lenses according to the present invention mayalso comprise stabilization features other than the uniform thicknessballast arrangement. For example, the peripheral zone may include aflattened region for dynamic stabilization, or the lens may incorporatea periballast stabilization outside of the central optic.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

1. A contact lens, comprising: a contact lens body having a generallyspherical base curvature with a convex anterior face, a concaveposterior face, and a peripheral edge therebetween with a peripheralzone being defined adjacent the peripheral edge of the anterior facethat is tapered thinner toward the peripheral edge of the lens body, anoptic zone being defined generally in the middle of the lens body, thebody having a thickness between the anterior face and the posterior faceand being non-axi-symmetric so as to define a superior edge and aninferior edge, with a vertical meridian being defined from the superioredge toward the inferior edge and a horizontal meridian being definedperpendicular thereto; an inner zone on the anterior face circumscribedby the peripheral zone and surrounding the optic zone, wherein the innerzone comprises a superior portion between the optic zone and thesuperior extent of the inner zone, an inferior portion between the opticzone and the inferior extent of the inner zone, and an intermediateportion between the superior and inferior portions; a ballast portiondefined on the anterior face radially inward from the peripheral zone ofthe lens body wherein in at least a part of the ballast portion thethickness of the lens body increases parallel to the vertical meridianfrom the superior edge toward the inferior edge, the ballast portionincluding a series of consecutive horizontal cross-sections exclusive ofthe optic zone each having a substantially uniform thickness; andwherein the ballast portion is defined within one or more of thesuperior, intermediate, and inferior portions and spans a distance alongthe vertical meridian of at least a fraction of the smallest dimensionof the superior, intermediate, and inferior portions as measured alongthe vertical meridian.
 2. The contact lens of claim 1, wherein theballast portion is provided on the entire inner zone including the opticzone.
 3. The contact lens of claim 1, wherein the ballast portion isprovided on the entire inner zone except for the optic zone.
 4. Thecontact lens of claim 1, wherein the ballast portion spans a distancealong the vertical meridian of at least 20% of the smallest dimension ofthe superior, intermediate, and inferior portions as measured along thevertical meridian.
 5. The contact lens of claim 1, wherein the ballastportion spans a distance along the vertical meridian of at least 50% ofthe smallest dimension of the superior, intermediate, and inferiorportions as measured along the vertical meridian.
 6. The contact lens ofclaim 1, wherein the ballast portion is defined wholly within only oneof the superior, intermediate, and inferior portions.
 7. The contactlens of claim 1, wherein the ballast portion is defined wholly withinonly two of the superior, intermediate, and inferior portions.
 8. Thecontact lens of claim 1, wherein the ballast portion is defined withinall three of the superior, intermediate, and inferior portions.
 9. Thecontact lens of claim 1, wherein the ballast portion spans a distancealong the vertical meridian extending all the way along the superior,intermediate, and inferior portions as measured along the verticalmeridian.
 10. The contact lens of claim 1, wherein the consecutivehorizontal cross-sections each has a substantially uniform thickness notvarying by more than about 30 μm or 20%, whichever is greater inabsolute terms.
 11. The contact lens of claim 1, wherein the consecutivehorizontal cross-sections each has a substantially uniform thickness notvarying by more than about 15 μm or 10%, whichever is greater inabsolute terms.
 12. The contact lens of claim 1, wherein, along a 225°meridian, the distance between the inner zone and the peripheral edge isless than about 1.45 mm.
 13. The contact lens of claim 1, wherein, alonga 225° meridian, a rate of change of thickness in the tapered peripheralzone is less than about 250 μm/mm.
 14. The contact lens of claim 1,wherein the ballast portion is a prism ballast.
 15. The contact lens ofclaim 1, further including a cylindrical correction on either theanterior face or the posterior face.
 16. The contact lens of claim 15,wherein the cylindrical correction is provided on the posterior face,and wherein the optic zone of the anterior face comprises a sphericalcorrection.
 17. The contact lens of claim 1, wherein the inner zone isof substantially uniform radial width around the circumference of thelens.
 18. The contact lens of claim 17, wherein a band circumscribed bythe peripheral zone and around the optic zone is substantially annular,with a superior distance A being defined along the vertical meridian andwithin the inner zone from the optic zone to the peripheral zone, and aninferior distance B being defined along the vertical meridian and withinthe inner zone from the optic zone to the peripheral zone, and wherein0.25A≦B≦A.
 19. The contact lens of claim 1, wherein the body is a softcontact lens.
 20. The contact lens of claim 1, wherein the ballastportion is a periballast.
 21. The contact lens of claim 1, wherein thelens further incorporates a dynamic stabilization mechanism.
 22. Thecontact lens of claim 1, wherein the lens further incorporates anegative spherical power distance correction.
 23. The contact lens ofclaim 1, wherein the thickness of the lens body increases parallel tothe vertical meridian from the superior edge toward the inferior edgealong the entire ballast portion.
 24. A contact lens, comprising: acontact lens body having a generally spherical base curvature with aconvex anterior face, a concave posterior face, and a peripheral edgetherebetween with a peripheral zone being defined adjacent theperipheral edge of the lens, the body having a thickness between theanterior face and the posterior face and being non-axi-symmetric so asto define a superior edge and an inferior edge, with a vertical meridianbeing defined from the superior edge toward the inferior edge and ahorizontal meridian being defined perpendicular thereto; an inner zoneon the anterior face circumscribed by the peripheral zone with a ballastportion therein, wherein the thickness of the body increases parallel tothe vertical meridian from the superior edge toward the inferior edge inat least the ballast portion of the inner zone; and an optic zone on theanterior face defined generally in the middle of the inner zone, andwherein, along a 225° meridian, the radial dimension of the peripheralzone is less than about 1.4 mm.
 25. The contact lens of claim 24,wherein the peripheral zone tapers thinner toward the peripheral edge ofthe lens, and wherein along the 225° meridian, a rate of change ofthickness in the tapered peripheral zone is less than about 250 μm/mm.26. The contact lens of claim 25, wherein the rate of change ofthickness in the tapered peripheral zone is less than about 200 μm/mm.27. The contact lens of claim 24, wherein the maximum thickness along a225° meridian of the lens is between about 200-400 μm.
 28. The contactlens of claim 24, wherein the maximum thickness along a 225° meridian isbetween about 250-350 μm.
 29. The contact lens of claim 24, wherein theinner zone comprises a superior portion between the optic zone and thesuperior extent of the inner zone, an inferior portion between the opticzone and the inferior extent of the inner zone, and an intermediateportion between the superior and inferior portions, and wherein theballast portion is defined within one or more of the superior,intermediate, and inferior portions and has a series of consecutivehorizontal cross-sections exclusive of the peripheral zone and opticzone spanning a distance along the vertical meridian of at least 20% ofthe smallest dimension of the superior, intermediate, and inferiorportions as measured along the vertical meridian, wherein eachhorizontal cross-section has a substantially uniform thickness notvarying by more than about 30 μm or 20%, whichever is greater inabsolute terms.
 30. The contact lens of claim 24, wherein, along a 270°meridian, the distance between the inner zone and the peripheral edge isless than about 1.8 mm.
 31. A contact lens, comprising: a contact lensbody having a generally spherical base curvature with a convex anteriorface, a concave posterior face, and a peripheral edge therebetween witha peripheral zone being defined adjacent the peripheral edge of theanterior face that is tapered thinner toward the peripheral edge of thelens body, an optic zone being defined generally in the middle of thelens body, the body having a thickness between the anterior face and theposterior face and being non-axi-symmetric so as to define a superioredge and an inferior edge, with a vertical meridian being defined fromthe superior edge toward the inferior edge and a horizontal meridianbeing defined perpendicular thereto; and a ballast portion defined onthe anterior face radially inward from the peripheral zone of the lensbody wherein in at least a part of the ballast portion the thickness ofthe lens body increases parallel to the vertical meridian from thesuperior edge toward the inferior edge, the ballast portion including aseries of consecutive horizontal cross-sections exclusive of the opticzone each having a substantially uniform thickness not varying by morethan 30μ or 20% whichever is greater in absolute terms.
 32. The contactlens of claim 31, wherein the consecutive horizontal cross-sections eachhas a substantially uniform thickness not varying by more than about 15μm or 10%, whichever is greater in absolute terms.
 33. A contact lens,comprising: a contact lens body having a generally spherical basecurvature with a convex anterior face, a concave posterior face, and aperipheral edge therebetween with a peripheral zone being definedadjacent the peripheral edge of the anterior face that is taperedthinner toward the peripheral edge of the lens body, an optic zone beingdefined generally in the middle of the lens body, the body having athickness between the anterior face and the posterior face and beingnon-axi-symmetric so as to define a superior edge and an inferior edge,with a vertical meridian being defined from the superior edge toward theinferior edge and a horizontal meridian being defined perpendicularthereto; an inner zone on the anterior face circumscribed by theperipheral zone and surrounding the optic zone, wherein, along a 225°meridian, the distance between the inner zone and the peripheral edge isless than about 1.45 mm; and a ballast portion defined on the anteriorface radially inward from the peripheral zone of the lens body whereinin at least a part of the ballast portion the thickness of the lens bodyincreases parallel to the vertical meridian from the superior edgetoward the inferior edge, the ballast portion including a series ofconsecutive horizontal cross-sections exclusive of the optic zone eachhaving a substantially uniform thickness.
 34. A contact lens,comprising: a contact lens body having a generally spherical basecurvature with a convex anterior face, a concave posterior face, and aperipheral edge therebetween with a peripheral zone being definedadjacent the peripheral edge of the anterior face that is taperedthinner toward the peripheral edge of the lens body, an optic zone beingdefined generally in the middle of the lens body, the body having athickness between the anterior face and the posterior face and beingnon-axi-symmetric so as to define a superior edge and an inferior edge,with a vertical meridian being defined from the superior edge toward theinferior edge and a horizontal meridian being defined perpendicularthereto, wherein, along a 225 meridian, a rate of change of thickness inthe tapered peripheral zone is less than about 250μ/mm; and a ballastportion defined on the anterior face radially inward from the peripheralzone of the lens body wherein in at least a part of the ballast portionthe thickness of the lens body increases parallel to the verticalmeridian from the superior edge toward the inferior edge, the ballastportion including a series of consecutive horizontal cross-sectionsexclusive of the optic zone each having a substantially uniformthickness.
 35. A contact lens, comprising: a contact lens body having agenerally spherical base curvature with a convex anterior face, aconcave posterior face, and a peripheral edge therebetween with aperipheral zone being defined adjacent the peripheral edge of theanterior face that is tapered thinner toward the peripheral edge of thelens body; an optic zone being defined generally in the middle of thelens body, the body having a thickness between the anterior face and theposterior face and being non-axi-symmetric so as to define a superioredge and an inferior edge, with a vertical meridian being defined fromthe superior edge toward the interior edge and a horizontal meridianbeing defined perpendicular thereto; and an inner zone on the anteriorface circumscribed by the peripheral zone and surrounding the opticzone, wherein the inner zone is of substantially uniform radial widtharound the circumference of the lens; a ballast portion defined on theanterior face radially inward from the peripheral zone of the lens bodywherein in at least a part of the ballast portion the thickness of thelens body increases parallel to the vertical meridian from the superioredge toward the inferior edge, the ballast portion including a series ofconsecutive horizontal cross-sections exclusive of the optic zone eachhaving a substantially uniform thickness; and wherein a bandcircumscribed by the peripheral zone and around the optic zone issubstantially annular, with a superior distance A being defined alongthe vertical meridian and within the inner zone from the optic zone tothe peripheral zone, and an inferior distance B being defined along thevertical meridian and within the inner zone from the optic zone to theperipheral zone, and wherein 0.25A≦B≦A.
 36. A contact lens, comprising:a contact lens body having a generally spherical base curvature with aconvex anterior face, a concave posterior face, and a peripheral edgetherebetween with a peripheral zone being defined adjacent theperipheral edge of the anterior face that is tapered thinner toward theperipheral edge of the lens body, an optic zone being defined generallyin the middle of the lens body, the body having a thickness between theanterior face and the posterior face, a toric surface for cylindricalcorrection and being non-axi-symmetric so as to define a superior edgeand an inferior edge, with a vertical meridian being defined from thesuperior edge toward the inferior edge and a horizontal meridian beingdefined perpendicular thereto; and a ballast portion defined on theanterior face radially inward from the peripheral zone of the lens bodywherein in at least a part of the ballast portion the thickness of thelens body increases parallel to the vertical meridian from the superioredge toward the inferior edge, the ballast portion including a series ofconsecutive horizontal cross-sections exclusive of the optic zone eachhaving a substantially uniform thickness.